The art of electronic ink processing often involves compression or encoding algorithms for storing and processing data that represents a stroke entered through a pointer or pen device. Compression often involves down-sampling the source trajectory, and then encoding the remaining points using some statistical method. In decompressing the source trajectory, a decoder restores the down-sampled set of source points, then (optionally) does up-sampling to provide a smoother representation of decoded strokes. Systems using this approach are described in U.S. Pat. No. 6,101,280, entitled Method and Apparatus For Compression of Electronic Ink, invented by D. E. Reynolds, issued Aug. 8, 2000, and in PCT International Application WO 94/03853, entitled A Method and Apparatus For Compression of Electronic Ink, invented by J. S. Ostrem and published Feb. 17, 1994
Other schemes exist for processing electronic ink. In one past approach, the source trajectory that is identified as a stroke is modeled as a sequence of segments. To encode or compress, each segment is approximated using an analytical curve from some class (usually Bezier curves), and then the parameters of the segments' analytical representation are statistically encoded. To decompress, decoder restores the parameters of segments, then generates discreet representation of decoded strokes using analytical formulae for each segment. This can be done using an arbitrary sampling rate. A system using this approach is described in U.S. Pat. No. 5,473,742, entitled Method and Apparatus For Representing Image Data Using Polynomial Approximation Method and Iterative Transformation-Reparametrization Technique, invented by V. G. Polyakov et al and issued Dec. 5, 1995.
Systems using the second scheme usually provide better compression ratios and better quality of decompressed ink strokes. However, the modeling algorithms they employ tend to be computationally demanding.
Mobile computers, such as laptop, tablet or palm-sized computers usually have drastic performance constraints on the software they use. Such software should use the least possible number of CPU cycles to conserve battery energy. So it is reasonable to use the first compression scheme above for such platforms. The main drawback of this approach arises when trying to get a high compression ratio. In such cases, there is a need to considerably down-sampling the representation of source strokes. However, in the past, this approach has lead to a poor quality image for the decompressed ink strokes.